I don't currently have an iPhone or iPod/iPad, but I stumbled acrossLog In and wanted to share, because I know many do have Apple products. The article discusses 7+ free iOS apps for use in identifying birds via sight and also sound. I used a few different birding apps back when I had my iPod touches, and really liked the apps. I haven't downloaded one yet for my Samsung Galaxy Tablet, but I know there are also many free apps available in the GooglePlay store.
